Aquatic weeds and their utilization 337cattle contain 4% dried citrus pulp or cracked yellow dent corn (Bagnall et al.
1974).
Silage treated with formic acid as a preservative (about 2 L acid/ton pressed
water hyacinth) is usually superior to untreated silage as cattle feed. Studies
with other organic acid preservatives, e.g. acetic and propionic acids, have also
been successful.
Added carbohydrate also functions as an absorbent material that is necessary
because of the high water content of the weed. If highly absorbent additives
could be found, this may eliminate the need for preliminary dehydration (NAS
1976). In this respect, the use of chitin as an absorbent additive (section 6.8)
appears promising, but cost effectiveness of this application needs to be studied
on a case-by-case basis.
Human food
Aquatic plants can provide three types of food: foliage for use as a green
vegetable; grain or seeds that provide protein, starch or oil; and swollen fleshy
roots that provide carbohydrate, mainly starch. There are more than 40 species
of aquatic weeds that are edible.
Certain species having potential for more widespread use are Chinese water
chestnut (Eleocharis dulcis), water spinach (Ipomoea aquatica) (Figure 7.10),
water lilies and taro (Clocasia esculenta). Duckweeds, Spirodela and Lemna ,
which contain high protein content (over 30% of dry weight) warrant further
study. But before any waste recycling system is started, social acceptance and
possible public health hazards has to be investigated.
Figure 7.10 Water spinach, an aquatic plant that can be used for human consumption